The present invention relates to vascular catheters for use in medical procedures and, more particularly, to catheters having distal ends, tips or segments that can be remotely shaped, guided or steered. The present invention also relates to methods of making such catheters.
Catheters have been in common use in medical practice for many years. They are often used, for example, to probe locations inside a body of a patient which are otherwise unreachable without surgery. A catheter is first inserted into a vein, artery, or other structure or region of the body of the patient. The catheter is then guided to the area of concern by further inserting it into the patient""s body. As medical knowledge increases, more uses of catheters have been developed and these uses have become more complex so that the ability to accurately and selectively steer and control the positioning and shape of the distal portion of the catheter has become of extreme importance. For example, there is a need to use steerable catheters to supply or remove fluids or cells to or from various internal tissues of the patient and to apply or sense electrical signals to or from such tissues. Administered fluids may, for example, be in the form of a liquid suspension or gel containing a drug or other chemical used, for example, to treat or anesthetize the tissue.
In order to place the tip of the catheter in the correct location and position, it is often necessary or highly desirable to variously curve the catheter so that its distal portion will travel into the proper anatomical region or cavity as the catheter is inserted into the patient, or so that its distal portion conforms to the shape of the anatomical cavity so that the catheter""s distal portion contacts the tissues of interest. After the distal portion has been so curved, it is also often desirable to rotate the catheter while maintaining the curvature of the distal region so that the intended portion of the catheter can then approach and/or contact the tissues of interest. It is also important that the catheter be able to make firm contact with the tissue of interest to facilitate reliable transmission or sensing of an electrical current to or from the tissue and/or reliable application or removal of fluid by the catheter.
A catheter which addresses some of the above problems is disclosed in U.S. Pat. No. 5,190,050, the entire disclosure of which is expressly incorporated by reference herein. In the catheter disclosed therein, the distal portion easily and reliably bends or twists in an angular orientation or curve that is selectively controllable. The distal end of the catheter is hollow and has at least two flat planar rigid juxtaposed shims mounted therein. The distal ends of the shims are attached to one another while the proximal end of at least one of the shims is attached to a pull cable and ultimately to the catheter handle. When a doctor or other user manipulates the catheter handle so that the catheter translates distally with respect to the handle, one of the shims follows the distal translation while the other shim retains its longitudinal distance from the handle causing the other shim and the associated distal portion of the catheter to longitudinally bend. Because of the planar shape of the shims and their rigidity, the bending of the distal portion of the catheter is always identical in direction, although varying in degree proportionally to the magnitude of the manipulation of the catheter handle, and is in a single plane of movement. The distal portion of the catheter can also optionally carry contact electrodes to transmit electrical pulses to or from tissue of the patient""s body or can be made to pump fluids into or out of the body of the patient. Although the catheter disclosed in U.S. Pat. No. 5,190,050 is reliable, completely functional and useful for many applications, it is not able to assume a shape having a curvature in more than one plane.
There are certain internal passages or chambers in the body which are not easily accessible to a catheter that can bend in only one plane. In the heart, for example, when it is desired to apply electrical pulses to, detect electrical signals from, or to introduce or extract fluids to or from the mitral or tricuspid valve annulus, the tip of a catheter must be curved in two planes in order to properly contact the desired tissue. When the steerable catheter disclosed in U.S. Pat. No. 5,190,050 is used for this particular application, a doctor typically introduces the tip of the catheter into the heart""s atrium and adjusts the catheter""s handle to cause the tip to deflect in its single plane of deflection. The distal portion of the catheter""s tip is then manipulated, either by rotation, by further insertion, or by a combination of both so that it contacts and is wedged against certain tissues and/or tissue walls within the heart. As a result, a proximal portion of the tip of the catheter, which does not contain the sandwiched juxtaposed rigid shims, is caused through such contact or abutment with tissue walls to assume a curve or bend in a plane that is different from the deflection plane of the distal end of the catheter""s tip. As a result of this double twist in the catheter""s tip, the catheter can than be further inserted so that it enters the mitral or tricuspid valve annulus. The second twist in the tip of the catheter, however, is not fixed or locked, is not readily controllable or selectively attainable, and is not pre-programmed into the catheter. As a consequence, the catheter tip manipulations needed to attain the desired catheter tip shape requires substantial experience and skill.
The multiform twistable tip deflectable catheter disclosed in U.S. Pat. No. 5,358,479, the entire disclosure of which is expressly incorporated by reference herein, employs a single shim with at least one transverse or lateral twist which enables the tip of the catheter tube to assume a lockable pre-programmed curvature in more than one plane. Although this catheter is also reliable, completely functional and useful for many applications, its twisted shim design places some limit on the particular shapes that the catheter tip can assume.
The conformable catheter of the present invention broadly comprises a catheter handle, an elongated catheter tube, and the distal tip portion of the catheter tube, which is capable of assuming a desired pre-programmed shape. The catheter tube, which is preferably a hollow, rigid, reinforced tube, is sufficiently long to be inserted into a patient to reach a body cavity of interest, such as the heart.
The catheter""s tip portion is preferably made of a softer material so that it is more flexible than the catheter tube. A plurality of electrical contact plates or bands are mounted onto or around the outer surface of the catheter""s tip portion. The electrical contact plate are connected to wires which pass through the entire length of the catheter tube and through the handle where they may be separately connected to a plug connectable to signal sensors or to an electrical power source. A wire member is disposed within the core of the catheter""s tip portion, preferably extends through its entire length. The wire member is formed of a material that will assume a pre-programmed shape after pre-shaping and heat treatment and subsequent heating, such as a shape-memory binary nickel-titanium alloy (about 49.0 to about 50.7% titanium) or ternary nickel-titanium alloys containing other elements, such as chromium. Suitable shape-memory alloys include those commercially known as xe2x80x9cnickel-titaniumxe2x80x9d, xe2x80x9ctitanium-nickelxe2x80x9d, xe2x80x9cTee-nnexe2x80x9d, xe2x80x9cMemoritexe2x80x9d, xe2x80x9cNitinolxe2x80x9d, xe2x80x9cTinelxe2x80x9d and xe2x80x9cFlexonxe2x80x9d. The wire member is preferably electrically connected by one or more wires extending through the catheter tube and the handle to another plug which is connectable to an electrical power supply and optionally a microprocessor.
A plurality of buttons mounted to the handle are employed by the user to control heating of the wire member or connection of the electrical contact plates, or both. Some of the buttons may be rheostatically controlled such that the amount of electrical power to flowing in the circuit controlled by the button is adjustable.
To pre-program the shape of the wire member, prior to assembly of the catheter, the wire member is wound around a shaped, heat resistant fixture. A groove is formed in the outer surface of the fixture, sized and shaped so that the wire to become the wire member can be mounted therein. After winding the wire member around the fixture, the wire member is secured in place. To control heat treatment of the wire member, the fixture may then be mounted within a heat sink shell. By varying the composition of the wire member, the duration of heat treating, the temperature of the oven, and the configurations of the heat sink shell, or even by eliminating the heat sink entirely, the activation properties of the wire member may be varied, i.e., the temperature at which the portions of the wire member assume their pre-programmed shape. The assembly is then placed in a preheated oven and heated for a predetermined time. Heating of the wire member is continued until the temperature of the wire member exceeds the temperature at which the shape of the wire member on the fixture becomes programmed into the wire member. The entire assembly is then cooled and the wire member is unwound from the fixture and straightened. Preferably, at least one electrically conducting wire is then attached to the wire member, although more than one wire may be attached to the wire member at various points. The wire member is then preferably attached to a stainless steel spring, wrapped in a heat shrink electrical and thermal insulation sheath, and inserted into central lumen of the catheter so that the wire member is located at the catheter""s tip.
In operation, after the catheter""s distal tip portion is inserted into the desired point in the body or vessel at which the catheter is to be used, the wire member is activated by heating it electrically thereby causing the catheter""s tip portion to assume the pre-programmed curved or bent shape from its normally straight, generally linear disposition. Activation is preferably accomplished by connection of electric power to the wire member by activation of one of the buttons on the catheter handle. The electrical power causes the temperature of the wire member to rise so that it transfigures to a substantially rigid contoured condition, assuming substantially the same shape that it had during heat treatment when it was wrapped around the fixture. Various pre-programmed shapes can be selected to conform to various body cavities, such as, for example, a conical spiral to substantially conform to the heart""s left ventricle and an egg-shaped spiral to conform to the shape of the right atrium of the heart.
Upon electrical deactivation of the catheter""s tip portion, the temperature of the wire member decreases and, at the same time its rigidity decreases so that the catheter""s tip portion may conform and contact the walls of the body cavity being examined or treated with the catheter.
The shape of the tip portion of the catheter is thus electrically controlled, allowing it to assume its pre-programmed shape or to become deformable or limp simply by appropriate connection or disconnection of the electrical power.
By having different segments of the wire member individually controllable, i.e., by connection of more than one wire at different segments of the wire member, the user can activate different segments thereof at different times or rates. A rheostat control may be used to activate the wire member at any rate desired.
The wire member may be heated by applying an electrical signal thereto or alternatively, since the wire member will assume its pre-programmed shape merely upon heating, by heating the catheter""s tip portion in other ways, such as, for example, by using a laser that may or may not form a part of the catheter""s tip, non-invasive microwave heating of the catheter""s tip, or heating of the catheter""s tip by infusing heated fluid either through the catheter or from a source separate from the catheter.
The catheter""s tip is thus able to assume a three-dimensional shape to contact tissues at a variety of discrete locations within a body cavity. Each of the electrical contact plates on the catheter""s tip may be individually controlled so that each can be positioned to contact different tissues. Consequently, the electrical measurements taken may be used to generate a three-dimensional image of the electrical properties of the tissue being examined, thereby aiding medical diagnosis.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are intended solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.